Method for improving performance of an ink jet bar code printer

ABSTRACT

This invention improves the printing of bar codes by an ink drop printer, by providing a cure for the problem created by the aerodynamic effects on ink droplets as they are directed toward the print receiving surface.

United States Patent [191 Apr. 1,1975

Stone [54] METHOD FOR IMPROVING 3,596,275 7/1971 Sweet 346/75 XPERFORMANCE OF AN INK JET BAR 3,596,276 7/l97l Lovelady et a1. 346/75 XCODE PRINTER [75] Inventor: Joseph J. Stone, Northbrook, 11]. PrimaryExaminer-Joseph W. Hartary i Attorney, Agent, or Firm-Freilich,Wasserman, Rosen [73] Assignee. A. B. Dick Company, Chicago, Ill. &Fernandez Lindenberg [22] Filed: Jan. 14, 1974 [21] Appl. No.: 432,870

[57] ABSTRACT [52] US. Cl. 346/1, 346/75 This invention improves thepriming f b codes by [51] Int. Cl. Gold 18/00 an ink drop primer, byproviding a cure for h prob [58] Field of Search 346/75 lem created bythe aerodynamic effects on ink drop lets as they are directed toward theprint receiving sur- [56] References Cited f UNITED STATES PATENTS3,562,757 2/1971 Bischoff 346/75 X 5 Claims, 4 Drawing Figures D /ACONVERTERS JO 5 itztsisevs DROP bYNG RATE GATE. DROP COUNTER 56 CLOCKCARCU IT $OUI?C.E PE ET CF- 5 2e POTENTIAL 05C 5 4o 1 52. r 22 i 24 2s 4DATA WRiTE RE$ERVOiR TRANS" MM SOURCE g QE DueER =9 30 T 7 DROPCOLLECTOR PATENTEU AFR I I975 SHEET 1 0F 2 TO DUMP METHOD FOR IMPROVINGPERFORMANCE OF AN INK JET BAR CODE PRINTER BACKGROUND OF THE INVENTIONThis invention relates to ink drop printers and more particularly to animproved method and means for printing bar codes.

One of the current applications for ink drop printers is directed to theprinting of machine readable bar codes on packages, such as mailpackages. These machine readable bar codes are thereafter read for thepurpose of enabling the automatic sorting of these packages. To producea vertical bar requires the use of eight to ten droplets of ink. In apreferred configuration, a stationary ink jet nozzle produces thesedroplets and propels them towards a moving package surface. Appropriateelectrical charges are generated for each droplet so that they aredeflected in an upward scanning direction in their flight towards thepackage surface.

It is important, in the production of straight bars, that the sequenceof ink droplets reach the recording surface in such a manner thatapproximately uniform time intervals exist between adjacent droplets. Asignificant variation in the time interval of one drop, as compared tothe intervals between others, permits and package surface to movehorizontally by a significant amount before the ink drop impinges uponit. This produces horizontal displacements and unacceptable bar codes.

OFJECTS AND SUMMARY OF THIS INVENTION An object of this invention is theprovision of a method and means for compensating for the errorintroduced by aerodynamic effects on an ink drop bar code printer.

Another object of this invention is the provision of a method and meansfor improving bar code printing by an ink drop printer.

Still another object of this invention is the provision ofa novel andimproved method and means for operating an ink drop bar code printer.

The aerodynamic effect which causes unacceptable .bar code printing isthat the first drop of a group of droplets needed for printing a barcode has to pass through undisturbed air, from the drop forming nozzleto the receiving substrate. The droplets which come behind it areeffectively flying through air which has already been disturbed. Thefirst drop is slowed to the greatest extent, the second drop is notslowed as much as the first drop and the third drop still less. As aresult, the first drop of a stream falls behind the other drops so thatthe paper which is moving horizontally moves to such an extent that thedrop does not fall in line to assist in forming a proper straight barcode. Alternatively, the first drop can fall behind to the extent whereit will be caught up to by the second drop and they merge to form asingle larger drop which produces an enlarged spot on the paper.

To eliminate this effect, second and third drops are dumped or deflectedso that they will be returned to the inkreservoir and will notparticipate in the printing. The first drop will still fall backrelative to the following drops because of the increased aerodynamicdrag. It has been found that the amount that the first drop falls back,when the second and third drops are eliminated, is such that it fallsback into line with the fourth drop of an ink drop stream whereby aperfectly acceptable bar code is achieved by printing with the first,fourth, fifth, sixth, etc. drops. Obviously, the number of dropsgenerated for printing a particular bar is increased by two in order toprovide the bar with the proper length and to make up for theelimination of the second and third drops.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are schematicillustrations of aerodynamic effects caused on a drop in flight.

FIG. 3 is a block schematic diagram of a circuit arrangement which maybe used for carrying out this invention.

FIG. 4 is an illustrative waveform drawing.

DESCRIPTION OF THE EMBODIMENT OF THE INVENTION FIG. 1 is a schematicillustration of a typical flight error problem which is encountered withequipment of the type indicated. To produce a proper bar code, droplets1 through 4 (along with the remaining droplets of the bar code, whichare not shown here) should fall along the dashed straight line 10. Thedroplets are represented by the dotted circles and numbered 1 through 4.The first drop, however, since it is effectively the path breaker,passes through undisturbed air. The following droplets do not have asmuch aerodynamic drag because of the pre-passage of the first drop. As aresult, the first drop slows down more rapidly than those that followit. The result can cause timing errors in the flight time of thedroplets to the paper surface and the bar code has a resultanthorizontal curvilinear distortion. It is also possible, as representedby the circle with 1 and 2 therein, that the droplets combine to form asingle large droplet, which produces an enlarged spot on the papersurface.

FIG. 2 illustrates the method and means whereby compensation is providedfor the aerodynamic problem. As represented by FIG. 2, the stream ofdrops is generated as before. The first drop, as before, encounters anaerodynamic drag and falls behind its intended position. However,droplets 2 and 3 are directed to the dump or collector for unused inkdrops, permitting droplets 4 and 5 to assume the spatial positionpreviously intended for the second and third droplets. The other dropsfall in line so that a straight vertical bar is printed on the surfaceof the paper. This method of operating the ink drop printer permits theslowing down to occur as previously indicated and regroups the firstdrop into a linear relationship with a following sequence of dropswhereby the increased flight time of the first drop has been anticipatedand compensated forQIn the illustration given, only two drops need to bedumped. In some cases, more or less than two may be dumped in order toachieve proper compensation.

FIG. 3 is a block schematic diagram of an arrangement for compensatingfor the aerodynamic flight problem encountered by the ink drops, asdescribed above. Also schematically shown in FIG. 3 is an ink dropwriting system of a well known type. This comprises an ink reservoir 20,which supplies ink under pressure to a nozzle 22. The nozzle isalternately constricted and permitted to expand by a transducer 24, at afrequency determined by an oscillator 26, whose output drives thetransducer.

A stream of ink is emitted from the nozzle 22, and in response to theaction by the transducer, breaks down into a stream of drops between twocharging plates 28, 30, which are spaced on either side of the droppath.

A charge is induced on each of the drops passing between plates 28, 30,having an amplitude determined by the voltage applied to the plates atdrop formation time. The stream of drops next passes between a pair ofdeflection plates 32, 34. These deflection plates have a fixed biasapplied thereto from a source of potential 36. As a result, a droppassing therebetween receives a vertical deflection determined by theinteraction of the electric field established between plates 32, 34, andthe charge on the drop.

Drops not required for writing are intercepted by a drop catcher 38after passing through the region between plates 32 and 34. The remainingdrops clear the barrier established by the drop catcher and aredeposited on the receiving surface 40, which is moving in the directionshown by the arrow. The location at which the drops are deposited isdetermined by the charges which were applied to the drops as well as theeffects of aerodynamic drag, as described above.

In accordance with this invention, a drop rate clock circuit 42, whichis a clock circuit whose clock pulse output is used to determine thedesired drop rate, has its output applied to a sync gate circuit 44 aswell as to the oscillator 26, which is synchronized thereby. The syncgate circuit 44 is enabled to pass clock pulses in the presence of awrite command signal from a write command signal source 46, and when theoutput of an inverter 48, which is connected thereto is high. Theinverter output is high only when a drop counter 50 does not provide an11 count output. The 11 count output of the counter is connected to theinverter 48. By way of example, the counter is shown to have elevencounts, three more than the number of drops required to write a bar.This is to be considered as exemplary only.

The write command signal is provided by the output signal from a datasource 52. The data source provides an output which determines the barcode to be written.

In the presence of a write command signal, the drop counter 50 is resetto its first count whereby the sync gate circuit is enabled and the dropcounter can commence counting clock pulses. All of the count outputs ofthe drop counter except the second and third count outputs are connectedto a digital to analog converter 53, the output of which is applied to asumming amplifier 54. The digital to analog converter and summingamplifier convert the counts into a stair-step waveform 56 of the typeshown in FIG. 4. It will be noted that the second and third counts ofthe counter are not connected to the digital to analog converter. Thus,as shown by the waveform 56 in FIG. 4, there are no correspondingoutputs for the second and third counts of the counter, but the outputoccurring in response to the fourth count output is twice as large asthe output occurring in response to the first count output and thefollowing outputs increase incrementally. A stair-step charging voltagewaveform 58 illustrative of the prior art is also shown in FIG. 4 andmay be compared with waveform 56.

The output of amplifier 54 is applied to the charging plates 28, 30, andeach drop is thereby charged to an amplitude level determined by thecount occurring at the time it is formed. When the counter 50 reachesits eleventh count, the inverter 48 output goes low, the sync gate 44 isclosed. The eleventh count output of the counter is not connected to theamplifier 54 and therefore any drops occurring now will have no chargeand be caught by the drop collector. Upon receipt of the next writecommand signal, the circuit described operates to write another bar.

As a result of no charge being applied to the second and third drops,they are dumped. That is, they receive no upward deflection when passingthrough the field established between electrodes 32 and 34 and thereforedo not get past the barrier established by deflector of the dropcollector 38. Therefore, as previously explained, due to the aerodynamicdrag on the first drop, it slows down until it is in proper positionrelative to the fourth, fifth and other drops to form a perfect bar inthe bar code.

While the foregoing description shows a withholding of the charge to thesecond and third drops, it is considered within the ability of thoseskilled in the art to dispose of the unwanted drops by applying a loweramplitude charge than is applied to the other drops, or a negativecharge. Thus, this is to be considered as being within the scope of thepresent invention and the claims. Also, while the drop rate clock 42 isshown as synchronizing the oxcillator 26, if desired, the alternative,using the oscillator 26 to synchronize the drop rate clock, may be used.

There has accordingly been described and shown herein a novel and usefulmethod and means for compensating for the adverse effects of aerodynamicdrag on an ink drop stream.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In an ink drop printer of the type wherein a stream of drops isemitted for printing a bar in a bar code, and wherein the leading dropsin the stream are retarded, due to aerodynamic effects to therebyadversely affect the printing, the method of compensating for theadverse aerodynamic effects comprising generating a plurality of inkdrops to form a stream, projecting said stream of ink drops in a pathtoward a receiving substrate for printing a bar thereon,

removing from each stream of drops those drops immediately following thefirst of the drops in each stream which due to aerodynamic effectscannot align themselves with the remaining drops in said stream forprinting a bar in a bar code, and

deflecting the remainder of the drops in said stream of drops to desiredlocations on said substrate. 2. A method as recited in claim 1 whereinsaid step of removing one or more of the drops following the first dropin said stream of drops, and deflecting the remaining drops in saidstream to desired locations on said substrate comprises interceptingsaid one or more drops following said first drop prior to reaching saidsubstrate,

applying charges to the remaining drops in said stream representative ofthe locations desired to be reached by said drops on said substrate, and

establishing an electric field in the path of said drops toward saidsubstrate through which said drops must pass to reach desired locationson said substrate.

3. In an ink drop printing system of the type wherein each bar in a barcode is printed by projecting a stream of ink drops in a path throughthe air toward a receiving substrate, and the leading drops in saidstream of ink drops, due to aerodynamic drag, are slowed in theirflight, thereby causing defective printing, the improvement comprisingmeans for projecting successive streams of drops toward said substratefor correctly printing bars in a bar code, including means for removingthose drops from each stream of drops immediately following the firstink drop in a stream of ink drops which, due to aerodynamic effects willnot properly align themselves with the remaining ink drops in said inkdrop stream for printing a bar in a bar code to thereby eliminate thedefective printing caused by aerodynamic drag. 4. In an ink dropprinting system as recited in claim 3 wherein said means for removingthose drops from each stream of said ink drops following said first inkdrop in an ink drop stream includes means for applying a charge to eachof said ink drops in an ink drop stream having an amplitude inaccordance with the location it is desired for each drop to reach on thesurface of the receiving substrate,

means for establishing an electric field between said means for chargingsaid drops in a stream and said substrate, and

means within said means for applying a charge, for

withholding a charge from each of said predetermined number of drops, toinsure that they are deflected out of the path which the remaining dropsin said stream take when passing through said electric field.

5. in an ink drop printer of the type wherein a stream of drops isemitted for printing a bar in a bar code, and wherein one or more of theleading drops in the stream are retarded, due to aerodynamic effectthereby adversely affecting the printing, apparatus for compensating forthe adverse aerodynamic effect comprising means for projecting a streamof drops in a path towards a receiving substrate to print a bar thereon,

means along said path for intercepting drops having a predeterminedcharge and preventing them from reaching said substrate,

means, along said path and upstream of said means for interceptingdrops, for charging each drop with a charge for deflecting each drop toa desired location on said substrate and for charging with saidpredetermined charge successive drops following the first drop in astream, which, due to aerodynamic effects will not align themselves withthe remaining drops in said stream for printing a bar in a bar code,whereby said predetermined charged drops are intercepted by said meansfor intercepting, and

means for establishing an electric field along said path for deflectingeach of said drops in accordance with the charge applied thereto,whereby said first drop aligns itself with the remaining drops reachingsaid substrate to thereby eliminate said adverse printing effect.

1. In an ink drop printer of the type wherein a stream of drops isemitted for printing a bar in a bar code, and wherein the leading dropsin the stream are retarded, due to aerodynamic effects to therebyadversely affect the printing, the method of compensating for theadverse aerodynamic effects comprising generating a plurality of inkdrops to form a stream, projecting said stream of ink drops in a pathtoward a receiving substrate for printing a bar thereon, removing fromeach stream of drops those drops immediately following the first of thedrops in each stream which due to aerodynamic effects cannot alignthemselves with the remaining drops in said stream for printing a bar ina bar code, and deflecting the remainder of the drops in said stream ofdrops to desired locations on said substrate.
 2. A method as recited inclaim 1 wherein said step of removing one or more of the drops followingthe first drop in said stream of drops, and deflecting the remainingdrops in said stream to desired locations on said substrate comprisesintercepting said one or more drops following said first drop prior toreaching said substrate, applying charges to the remaining drops in saidstream representative of the locations desired to be reached by saiddrops on said substrate, and establishing an electric field in the pathof said drops toward said substrate through which said drops must passto reach desired locations on said substrate.
 3. In an ink drop printingsystem of the type wherein each bar in a bar code is printed byprojecting a stream of ink drops in a path through the air toward areceiving substrate, and the leading drops in said stream of ink drops,due to aerodynamic drag, are slowed in their flight, thereby causingdefective printing, the improvement comprising means for projectingsuccessive streams of drops toward said substrate for correctly printingbars in a bar code, including means for removing those drops from eachstream of drops immediately following the first ink drop in a stream ofink drops which, due to aerodynamic effects will not properly alignthemselves with the remaining ink drops in said ink drop stream forprinting a bar in a bar code to thereby eliminate the defective printingcaused by aerodynamic drag.
 4. In an ink drop printing system as recitedin claim 3 wherein said means for removing those drops from each streamof said ink drops following said first ink drop in an ink drop streamincludes means for applying a charge to each of said ink drops in an inkdrop stream having an amplitude in accordance with the location it isdesired for each drop to reach on the surface of the receivingsubstrate, means for establishing an electric field between said meansfor charging said drops in a stream and said substrate, and means withinsaid means for applying a charge, for withholding a charge from each ofsaid predetermined number of drops, to insure that they are deflectedout of the path which the remaining drops in said stream take whenpassing through said electric field.
 5. In an ink drop printer of thetype wherein a stream of drops is emitted for printing a bar in a barcode, and wherein one or more of the leading drops in the stream areretarded, due to aerodynamic effect thereby adversely affecting theprinting, apparatus for compensating for the adverse aerodynamic effectcomprising means for projecting a stream of drops in a path towards areceiving substrate to print a bar thereon, means along said path forintercepting drops having a predeteRmined charge and preventing themfrom reaching said substrate, means, along said path and upstream ofsaid means for intercepting drops, for charging each drop with a chargefor deflecting each drop to a desired location on said substrate and forcharging with said predetermined charge successive drops following thefirst drop in a stream, which, due to aerodynamic effects will not alignthemselves with the remaining drops in said stream for printing a bar ina bar code, whereby said predetermined charged drops are intercepted bysaid means for intercepting, and means for establishing an electricfield along said path for deflecting each of said drops in accordancewith the charge applied thereto, whereby said first drop aligns itselfwith the remaining drops reaching said substrate to thereby eliminatesaid adverse printing effect.